The following references detail technologies applicable in connection with applicants' work.
U.S. Pat. No. 6,584,214 discloses how three-dimensional characteristics of a complex physical structure can be used to generate a unique identifier useful, e.g., in cryptography. In effect, the physical characteristics represent the basis of a “physical one-way hash function” that facilitates derivation of an identifier based on the structure (yet the structure cannot be reproduced given only the identifier).
Related work is detailed in the March, 2001, MIT thesis by Pappu, entitled “Physical One-Way Functions,” and in the related Pappu et al paper of the same name, published in the Sep. 20, 2002, issue of Science (Vol. 297, pp. 2026-2030).
Chen et al have noted that an inexpensive physical object can serve as a cryptographic element, if a random unique structure of the object (e.g., paper fiber) is accurately quantified. (“Certifying Authenticity via Fiber-Infused Paper,” ACM SIGecom Exchanges, Volume 5, Issue 3, April 2005, pages 29-37.)
Rodriguez et al have written about use of cell phones and like devices for validation of document security features. (“On the Use of Mobile Imaging Devices for the Validation of First- and Second-Line Security Features,” SPIE Vol. 6075, February, 2006.)
WIPO patent publication WO 2005/106783 details how the propagation of sonic vibrations through an inhomogeneous medium—such as a card with embedded irregularities—can generate data by which the medium can be uniquely identified.
A number of patent documents teach how a medium can be uniquely identified by reference to its inherent physical characteristics, such microscopic grain structure, optical characteristics, or structural characteristics. Examples include US20050190914, US20050210255, US20030035564, US20050262350, WO0065541, WO03030105 (corresponding, e.g., to U.S. applications 60/317,665, and 60/394,914), and WO03087991 (corresponding, e.g., to 60/371,073).
Arrangements in which data is represented by reference to angles (e.g., angular symbologies) are taught, e.g., in US2003026448 and US20050285761.
U.S. Pat. No. 6,987,568 details a method and apparatus for measuring bidirectional reflectance distribution function.
U.S. Pat. No. 6,421,453 shows that gestures can be employed in identification applications.
To provide a comprehensive disclosure without unduly lengthening this specification, the documents identified herein (both above and below) are incorporated by reference.